/**
 * @extend Ext.data.IdGenerator
 * @author Don Griffin
 *
 * This class generates UUID's according to RFC 4122. This class has a default id property.
 * This means that a single instance is shared unless the id property is overridden. Thus,
 * two {@link Ext.data.Model} instances configured like the following share one generator:
 *
 *     Ext.define('MyApp.data.MyModelX', {
 *         extend: 'Ext.data.Model',
 *         idgen: 'uuid'
 *     });
 *
 *     Ext.define('MyApp.data.MyModelY', {
 *         extend: 'Ext.data.Model',
 *         idgen: 'uuid'
 *     });
 *
 * This allows all models using this class to share a commonly configured instance.
 *
 * # Using Version 1 ("Sequential") UUID's
 *
 * If a server can provide a proper timestamp and a "cryptographic quality random number"
 * (as described in RFC 4122), the shared instance can be configured as follows:
 *
 *     Ext.data.IdGenerator.get('uuid').reconfigure({
 *         version: 1,
 *         clockSeq: clock, // 14 random bits
 *         salt: salt,      // 48 secure random bits (the Node field)
 *         timestamp: ts    // timestamp per Section 4.1.4
 *     });
 *
 *     // or these values can be split into 32-bit chunks:
 *
 *     Ext.data.IdGenerator.get('uuid').reconfigure({
 *         version: 1,
 *         clockSeq: clock,
 *         salt: { lo: saltLow32, hi: saltHigh32 },
 *         timestamp: { lo: timestampLow32, hi: timestamptHigh32 }
 *     });
 *
 * This approach improves the generator's uniqueness by providing a valid timestamp and
 * higher quality random data. Version 1 UUID's should not be used unless this information
 * can be provided by a server and care should be taken to avoid caching of this data.
 *
 * See http://www.ietf.org/rfc/rfc4122.txt for details.
 */
Ext.define('Ext.data.UuidGenerator', function () {
    var twoPow14 = Math.pow(2, 14),
        twoPow16 = Math.pow(2, 16),
        twoPow28 = Math.pow(2, 28),
        twoPow32 = Math.pow(2, 32);

    function toHex (value, length) {
        var ret = value.toString(16);
        if (ret.length > length) {
            ret = ret.substring(ret.length - length); // right-most digits
        } else if (ret.length < length) {
            ret = Ext.String.leftPad(ret, length, '0');
        }
        return ret;
    }

    function rand (lo, hi) {
        var v = Math.random() * (hi - lo + 1);
        return Math.floor(v) + lo;
    }

    function split (bignum) {
        if (typeof(bignum) == 'number') {
            var hi = Math.floor(bignum / twoPow32);
            return {
                lo: Math.floor(bignum - hi * twoPow32),
                hi: hi
            };
        }
        return bignum;
    }

    return {
        extend: 'Ext.data.IdGenerator',

        alias: 'idgen.uuid',

        id: 'uuid', // shared by default

        /**
         * @property {Number/Object} salt
         * When created, this value is a 48-bit number. For computation, this value is split
         * into 32-bit parts and stored in an object with `hi` and `lo` properties.
         */

        /**
         * @property {Number/Object} timestamp
         * When created, this value is a 60-bit number. For computation, this value is split
         * into 32-bit parts and stored in an object with `hi` and `lo` properties.
         */

        /**
         * @cfg {Number} version
         * The Version of UUID. Supported values are:
         *
         *  * 1 : Time-based, "sequential" UUID.
         *  * 4 : Pseudo-random UUID.
         *
         * The default is 4.
         */
        version: 4,

        constructor: function() {
            var me = this;

            me.callParent(arguments);

            me.parts = [];
            me.init();
        },

        generate: function () {
            var me = this,
                parts = me.parts,
                ts = me.timestamp;

            /*
               The magic decoder ring (derived from RFC 4122 Section 4.2.2):

               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |                          time_low                             |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |           time_mid            |  ver  |        time_hi        |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |res|  clock_hi |   clock_low   |    salt 0   |M|     salt 1    |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |                         salt (2-5)                            |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         time_mid      clock_hi (low 6 bits)
                time_low     | time_hi |clock_lo
                    |        |     |   || salt[0]
                    |        |     |   ||   | salt[1..5]
                    v        v     v   vv   v v
                    0badf00d-aced-1def-b123-dfad0badbeef
                                  ^    ^     ^
                            version    |     multicast (low bit)
                                       |
                                    reserved (upper 2 bits)
            */
            parts[0] = toHex(ts.lo, 8);
            parts[1] = toHex(ts.hi & 0xFFFF, 4);
            parts[2] = toHex(((ts.hi >>> 16) & 0xFFF) | (me.version << 12), 4);
            parts[3] = toHex(0x80 | ((me.clockSeq >>> 8) & 0x3F), 2) +
                       toHex(me.clockSeq & 0xFF, 2);
            parts[4] = toHex(me.salt.hi, 4) + toHex(me.salt.lo, 8);

            if (me.version == 4) {
                me.init(); // just regenerate all the random values...
            } else {
                // sequentially increment the timestamp...
                ++ts.lo;
                if (ts.lo >= twoPow32) { // if (overflow)
                    ts.lo = 0;
                    ++ts.hi;
                }
            }

            return parts.join('-').toLowerCase();
        },

        getRecId: function (rec) {
            return rec.getId();
        },

        /**
         * @private
         */
        init: function () {
            var me = this,
                salt, time;

            if (me.version == 4) {
                // See RFC 4122 (Secion 4.4)
                //   o  If the state was unavailable (e.g., non-existent or corrupted),
                //      or the saved node ID is different than the current node ID,
                //      generate a random clock sequence value.
                me.clockSeq = rand(0, twoPow14-1);

                // we run this on every id generation...
                salt = me.salt || (me.salt = {});
                time = me.timestamp || (me.timestamp = {});

                // See RFC 4122 (Secion 4.4)
                salt.lo = rand(0, twoPow32-1);
                salt.hi = rand(0, twoPow16-1);
                time.lo = rand(0, twoPow32-1);
                time.hi = rand(0, twoPow28-1);
            } else {
                // this is run only once per-instance
                me.salt = split(me.salt);
                me.timestamp = split(me.timestamp);

                // Set multicast bit: "the least significant bit of the first octet of the
                // node ID" (nodeId = salt for this implementation):
                me.salt.hi |= 0x100;
            }
        },

        /**
         * Reconfigures this generator given new config properties.
         */
        reconfigure: function (config) {
            Ext.apply(this, config);
            this.init();
        }
    };
}());
